GEN 1 6.2 Misfire, no DTC(s), Plug oil fouled?

[other365]

Last year around this time I replaced all 16 plugs\wires, recently replaced boots and pellets on the coils. Truck currently has about 98k, less than 10k on the plug in the pics.

During my state inspection last month the tech noted he felt a misfire at idle. I figured he wasn't used to the Raptor's cam and dismissed it. Recently I got a new OBD2 cable and forscan, and confirmed I am indeed seeing misfires (mainly) on cylinder 8.

I pulled the top and bottom plug on 8 (nearest driver) - top plug looked new, bottom plug ceramic looks fouled with oil/oil on the threads? I replaced the bottom plug with a new spare. I don't think I am consuming oil but haven't driven the truck a ton this last year to notice.

I had initially replaced the coil with an NGK spare/cleared PCM but no change - the misfires happen at cold idle or at a steady ~1500 rpms when warm and cause a slight shake. They have never triggered a code but I can rack up about 10-30 misfires in 15mins when trying to replicate them on purpose. Never a misfire counted when driving normally.

Unfortunely I broke the plug wire getting it off the bottom and cant find my old spare, so will have to wait until tomorrow to see if the new plug\wire stops the misfire (at least temporarily). The snap ring that goes over the electrode stayed on the plug when I pulled on the boot.

Hoping it was just a bad wire all along... I am sort of nervous because I just spent over >2k ordering deavers\shackles\bump pads\geisers.

What do you guys think? None of my original plugs had oil on them.

I also replaced the canister purge valve earlier on cause I'm dumb and fired the cheap parts cannon, I had read it could cause idle quality issues.

Mode 6 export from Forscan on Cyl8 - raw file attached.

[Misfire Cylinder 8 Data]

EWMA misfire counts for last 10 drive cycles
MID: A9
TID: B
Value: 0 Counts
Min: 0 Counts
Max: 65535 Counts
Misfire counts for last/current driving cycle (calculated)
MID: A9
TID: C
Value: 34 Counts
Min: 0 Counts
Max: 65535 Counts​

 

[MTF]

You can try a tighter gap, see if that helps.

 

[B E N]

Oil on threads is usually an indicator of valve cover gasket, o-ring, head gasket or rings. Since it is only the lower plug in that cylinder its very likely its just a valve cover gasket. Plug gap won't do much for oil fouling.

If that wire was bad that could be the source of the missfire, if it continues after the wire change there are further diagnostics that can be done without buying parts.

 

[Sozzy12]

Second the valve/cam cover gasket.

 

[other365]

Thanks for the feedback.

Valve cover would make sense if it were top plugs but there's no external oil seepage that I can see towards the bottom side. Not familiar with the cam seal but I will check it over real good.

I am working from home and don't drive much so I will pull the plug again in a few weeks and see how it looks.

 

[B E N]

You may not see external seepage, don't lose sleep over it. Check your oil when you fill up and if the misfire returns you can just change the plug again, rinse and repeat until your ready to do the gasket.

 

[zombiekiller]

I'd bet rings. Might want to scope the cylinder to check for scoring.

 

[BenBB]

Seems like a lot of fouling for 10k miles, and oil on the threads, that ain't good. Clearly not external so I'm leaning towards oil ring as @zombiekiller suggested, or maybe valve seal? What's the other plug on that cylinder look like? Got a compression tester? I thought I read something about the purpose of the second spark plug and I'm not finding shit now but for some reason I was thinking it had to do with emissions and/or combustion efficiency, either way it's not meant to burn off oil so something is amiss...

 

[other365]

I'd bet rings. Might want to scope the cylinder to check for scoring.

Seems like a lot of fouling for 10k miles, and oil on the threads, that ain't good. Clearly not external so I'm leaning towards oil ring as @zombiekiller suggested, or maybe valve seal? What's the other plug on that cylinder look like? Got a compression tester? I thought I read something about the purpose of the second spark plug and I'm not finding shit now but for some reason I was thinking it had to do with emissions and/or combustion efficiency, either way it's not meant to burn off oil so something is amiss...

From what I read the lower plug fires slightly after top plug to burn any left over fuel for emissions. The truck could theoretically run with no lower plugs, but would probably be unhappy. Put about 50 miles on it so far and no more misfires on 8 but it will take at least a few more weeks of driving to see if it fouls up again.

The top plug of cyl8 looked new\dry. Thats what really gives me hope that the bottom wire was flakey.

I will be ordering a compression tester and cheapy bore scope to have around for the next time I pull plugs. If anyone has any recommendations for > harbor freight quality but still budget let me know.

 

[B E N]

I would think a ring issue would show on both plugs.

Was there any oil on the plug boot?